The present invention relates to a process for producing an adsorbent block and a cleaning filter. The adsorbent block obtained by the process is preferably used in the cases where an offensive odor and harmful components are removed from a gas, such as air, and impurity ions are removed from a liquid, such as water. Therefore, the adsorbent block can be used as a cleaning filter in an air cleaning apparatus, such as an air cleaner, an air conditioner, in an water cleaning apparatus or the like, used in automobiles, home and factories.
For example, an air cleaner and the like are required to remove an offensive odor and the like from the air. Therefore, an adsorbent block removing an offensive odor and the like from the air is preferably used in a cleaning filter used therefor. As the adsorbent block, one having a honeycomb form formed by binding active carbon powder to have cells is known (Japanese Patent Laid-Open No. 5-242).
The conventional adsorbent block is produced roughly in the following manner. That is, a paste is prepared as a dispersion system having active carbon powder as a solid disperse phase in water as a liquid dispersion medium and containing a binder capable of dispersing various kinds of active carbon powder, and the paste is extruded to mold into a molded block in a honeycomb form. Water is then removed from the molded block to obtain an adsorbent block in a honeycomb form mainly comprising active carbon powder thus bound.
The resulting adsorbent block has continuous flow paths extending in a straight form as cells ascribed to the honeycomb form. Therefore, when the adsorbent block is used as a cleaning filter, for example, in an air cleaner, the air flows in the continuous flow paths, during which an offensive odor component and the like for having high adsorption efficiency in the resulting adsorbent in the air are adsorbed in minute pores to be removed.
However, in order to increase the contact area with an offensive odor component and the like in the foregoing conventional production process, the number of the continuous flow paths per unit area or unit volume is necessarily increased. In this case, when an adsorbent block in a honeycomb form is to be obtained, the number of the continuous flow paths per unit area or unit volume of the molded block of a honeycomb form itself is necessarily increased, and the production of an extruding die becomes difficult, so as to cause increase of the production cost.
This invention is made in view of the foregoing conventional circumstances, and has a problem to be solved to provide an adsorbent block having a high adsorption efficiency and can be produced at a low cost.
The first invention is a process for producing an adsorbent block comprising a first step of preparing a dispersion system comprising a liquid dispersion medium mainly having porous material powder as a solid disperse phase, and forming a molded block from said dispersion system, and
a second step of removing said liquid dispersion medium from said molded block to bind mainly said porous material powder, so as to obtain an adsorbent block formed to have continuous flow paths,
characterized in that said dispersion system contains a shrinkage agent that is capable of shrinking said molded block in said second step, and said shrinkage agent is capable of being swelled in a state of said dispersion system.
According to the test result of the inventors, in the case where a water absorbing resin or an agar component that are commercially available is employed as the shrinkage agent, and water is employed as the liquid dispersion medium, the water absorbing resin or the agar component is swelled with the liquid dispersion medium in the dispersion system. Accordingly, when the shrinkage agent is capable of being swelled in the state of the dispersion system, the molded block formed with the dispersion system is shrinked by removing the liquid dispersion medium in the second step. Therefore, according to the production process of the first invention, in the case where an adsorbent block in a honeycomb form is to be obtained, the molded block is shrinked in the second step even though the number of the continuous flow paths per unit area or unit volume of the molded block of a honeycomb form itself is not so increased, and the resulting adsorbent block has a number of the continuous flow paths per unit area or unit volume that is larger than the molded block.
Therefore, according to the production process of the first invention, the resulting adsorbent block has a large contact area with an offensive odor component and the like to have a high adsorbing efficiency. According to the production process of the first invention, since the mesh of a die for obtaining the molded block is not necessarily be fine, the production of the molded block is not difficult, and reduction of the production cost is realized.
Furthermore, when the shrinkage agent is contained in the dispersion system, the shrinkage of the molded block uniformly proceeds, and the dimensional stability of the molded block can be easily maintained.
According to a test result of the inventors, in the production process of the first invention, it is preferred that the shrinkage agent is employed in such a manner that the molded block is shrinked to a linear shrinkage ratio of from 5 to 25% per a molded block containing no shrinkage agent. The shrinkage agent that shrinks the molded block only to less than 5% per a molded block containing no shrinkage agent can exhibit substantially no effect of the invention. On the other hand, in the case of the shrinkage agent that shrinks the molded block to 25% or more per a molded block containing no shrinkage agent, molding becomes difficult, and the dimensional stability of the adsorbent block is difficult to be maintained due to distortion on shrinkage. A shrinkage agent capable of shrinking the molded block to from 7 to 20% per a molded block containing no shrinkage agent is preferred.
In the production process of the first invention, a high water absorbing resin having a large water holding ratio can be used as the shrinkage agent. As the high water absorbing resin, an acrylic series water absorbing resin, such as a starch-acrylic acid graft polymer, a crosslinked polyacrylate, a saponified product of a vinyl acetate-acrylate copolymer and the like, can be used. More specifically, a high water absorbing resin that can absorb water in a mass of from 100 to 1,000 times per unit mass is preferred. A high water absorbing resin that can absorb water in a mass of from 200 to 800 times per unit mass is more preferred, and a high water absorbing resin that can absorb water in a mass of from 400 to 700 times per unit mass is further preferred.
On the other hand, according to a test result of the inventors, in the case where a commercially available high water absorbing resin is employed as the shrinkage agent, and water is employed as the liquid dispersion medium, the high water absorbing resin can be swelled only in the dispersion system. It is considered that such a phenomenon occurs because high water adsorbing resin is crosslinked, even when a large amount of water is involved, the network structure of the linear molecules is stretched at all. In this case, therefore, the molded block is shrinked only at a low shrinkage ratio, and the improvement of the adsorption efficiency is limited. In order to avoid the phenomenon, it is necessary that the average particle diameter of the high water absorbing resin is decreased to solve the crosslinking of the high water absorbing resin, but the molded block is still shrinked at a low shrinkage ratio, and such a step is necessary that the high water absorbing resin is pulverized, whereby increase of the production cost occurs.
On the other hand, in the case where an agar component is employed as the shrinkage agent, and water is employed as the liquid dispersion medium, the agar component can be infinitely swelled in the dispersion system since it is easily dissolved in water. In more detail, while the extent of swelling is finite in cold water, it is infinitely swelled in warm water and hot water. Therefore, even when the number of the continuous flow paths per unit area or unit volume of the molded block itself is not so increased, the shrinkage agent shrinks the molded block to a high shrinkage ratio, and thus the resulting adsorbent block has an extremely larger number of the continuous flow paths per unit area or unit volume than the molded block.
Therefore, in the case where a shrinkage agent that can be infinitely swelled in the state of the dispersion system is employed as the shrinkage agent in the production process of the first invention, the resulting adsorbent block has an extremely large contact area with an offensive odor component and the like to exhibit an extremely high adsorption efficiency. In this case, since it is certainly not necessary to make fine the mesh of the die for obtaining the molded block, the production of the die truly involves no difficulty, and since the particle diameter of the shrinkage agent is not necessarily be considered, the reduction of the production cost is certainly realized. In other words, corresponding to the production line, the allowable cost and the like of the adsorbent block, the shrinkage ratio of the molded block, i.e., the adsorption efficiency of the adsorbent block, can be controlled as desired.
According to the analysis of the inventors, the agar component is one kind of hemicellulose contained in a cell membrane of algae. It had been considered that hemicellulose is a precursor of cellulose, but it has no relationship in structure and easily hydrolyzed with an acid or an enzyme as different from cellulose. It is considered that cellulose is added to the dispersion system to prevent cracks and strain of the molded block, but the shrinkage of the molded block is not considered in this case. The agar component comprises agarose as the main component and agaropectin as a small amount component. Agarose comprises alternating bonds of xcex2-D-galactose and 3,6-anhydro-xcex1-L-galactose, and is a neutral polysaccharide component having a high gelation power. In particular, the agar component having agarose as the main component is easily dissolved in warm water or hot water, and such a nature that it is gelled upon cooling. Therefore, when the shrinkage agent contains agarose, agarose effectively shrinks the molded block even when the number of the continuous flow paths per unit area or unit volume of the molded block itself is not so increased, and thus the resulting adsorbent block has an extremely larger number of continuous flow paths per unit area or unit volume than the molded block.
Therefore, in the production process of the first invention, when the shrinkage agent contains agarose, the resulting adsorbent block has an extremely large contact area with an offensive odor component and the like and thus has an extremely high adsorbing efficiency. In this case, since it is certainly not necessary to make fine the mesh of the die for obtaining the molded block, the production of the die truly involves no difficulty, and the reduction of the production cost is certainly realized. In other words, corresponding to the production line, the allowable cost and the like of the adsorbent block, the shrinkage ratio of the molded block, i.e., the adsorption efficiency of the adsorbent block, can be controlled as desired.
The dispersion medium system relating to the first step of the first invention contains the liquid dispersion medium and a solid disperse phase. The liquid dispersion medium is one that can constitute the dispersion system along with porous material powder as the solid disperse phase. The liquid dispersion medium relating to the first invention is necessarily one capable of being swelled with the shrinkage agent in the state of the dispersion system. When it is the case, the molded block is shrinked by removing the liquid dispersion medium from the molded block, so as to obtain the adsorbent block. As the liquid dispersion medium relating to the first invention, water is generally employed in the case where the shrinkage agent is an agar component. Water includes any of cold water, warm water and hot water. Depending on the selection of the shrinkage agent, a volatile solvent, such as an alcohol and the like, can be employed as the liquid dispersion medium. The agar component is dispersed in water along with the porous material powder, whereby a gelled dispersion system can be obtained. Thereafter, the dispersion system is subjected to molding, so as to mold a molded block having continuous flow paths.
The dispersion system relating to the first invention preferably contains a binder capable of binding the respective porous material powder. This is because the strength of the adsorbent block can be ensured thereby. In the case where water is employed as the liquid dispersion medium, a water soluble binder can be employed. As the water soluble binder, a cellulose derivative, such as methyl cellulose, carboxymethyl cellulose, ethyl cellulose, hydroxypropyl cellulose and the like, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and the like can be employed. In the case where an adsorbent block is used for removing impurity ions from water, a water resistant binder is used. The mixing ratio of the binder is not particularly limited, and the binder is preferably mixed at a mass ratio of from 1 to 50 parts by mass per 100 parts by mass of the mixture of the porous material powder and the shrinkage agent. It is more preferred that the binder is mixed at a mass ratio of from 2 to 30 parts by mass per 100 parts by mass of the mixture of the porous material powder and the shrinkage agent. It is further preferred that the binder is mixed at a mass ratio of from 5 to 15 parts by mass per 100 parts by mass of the mixture of the porous material powder and the shrinkage agent. The dispersion system may further contain a molding assistant, such as a dispersing agent, a wetting agent and the like.
As the second step of the first invention, in addition to air blowing and allowing to stand at room temperature, heat drying conducted at a temperature, at which combustion of the shrinkage agent and the like does not occur, freeze drying and the like can be employed.
The adsorbent block obtained by the first invention is formed to have continuous flow paths by binding mainly the porous material powder. The continuous flow path is a flow path that continues from an inlet to an outlet of the air or the like.
In the case where an adsorbent block of a honeycomb form is formed to have cells by the production process of the first invention, a cleaning filter can be obtained by the adsorbent block. The adsorbent block of the cleaning filter is produced by a production process comprising a first step of preparing a paste comprising water having mainly active carbon powder dispersed therein, and molding a molded block with the paste, and a second step of removing water from the molded block to bind mainly the active carbon powder. At this time, the paste contains a shrinkage agent that is capable of shrinking the molded block in the second step, and the shrinkage agent is capable of being swelled in a state of the paste.
The production process as a second invention comprises a first step of preparing a dispersion system comprising a liquid dispersion medium mainly having porous material powder as a solid disperse phase, and forming a molded block from the dispersion system, and
a second step of removing the liquid dispersion medium from the molded block to bind mainly the porous material powder, so as to obtain an adsorbent block formed to have continuous flow paths,
characterized in that the dispersion system contains a binder that is capable of binding the porous material powder and an area increasing agent that disappears by heating the molded block at a particular temperature, at which the binder does not disappear, and the second step comprises a liquid dispersion medium removing step of removing the liquid dispersion medium, and a heating step of heating the molded block at the particular temperature.
In the production process of the second invention, since the molded block is heated to the particular temperature in the heating step, the area increasing agent disappears, but the binder does not disappear. If the binder also disappears, the strength of the adsorbent block becomes deteriorated. If only the area increasing agent disappears in this manner, the pores are increased to that extent to increase the surface area of the continuous flow paths. Accordingly, such porous material powder that is present in a deep place of the wall constituting the continuous flow paths is also utilized to increase the contact area with the offensive odor component and the like, whereby an adsorbent block of an extremely high adsorption efficiency can be obtained. The disappearance of the area increasing agent may be effected by carbonization, which does not reach vaporization.
According to the production process of the second invention, in the case where an adsorbent block in a honeycomb form is to be obtained, the surface area of the continuous flow paths is increased in the area increasing step of the second step even though the number of the continuous flow paths per unit area or unit volume of the molded block of a honeycomb form itself is not so increased, and the resulting adsorbent block has a large contact area with the offensive odor and the like.
Therefore, according to the production process of the second invention, the resulting adsorbent block has a high adsorption efficiency. According to the production process of the second invention, since the mesh of a die for obtaining the molded block is not necessarily be fine, the production of the molded block is not difficult, and reduction of the production cost is realized.
As the second step of the second invention, in addition to air blowing and allowing to stand at room temperature, heat drying conducted at a temperature, at which combustion of the shrinkage agent and the like does not occur, freeze drying and the like can be also employed. It is preferred from the standpoint of efficiency that heat drying is conducted as the liquid dispersion medium removing step, and the heating step is continuously conducted.
In the case where the water soluble binder is employed, and water is employed as the liquid dispersion medium in the production process of the second invention, an agar component can be employed as the area increasing agent. The high water absorbing resin has a carbonization temperature that is substantially the same as the water soluble binder, and it is difficult that only the high water absorbing resin is made disappear, but the binder is not made disappear. From the standpoint, the agar component is carbonized and vaporized at a low temperature in comparison to the water soluble binder. This is because the agar component is obtained by extracting from seaweed naturally yielded. The water soluble binder is burnt at about 300xc2x0 C., and thus heating at the particular temperature lower than that temperature can be employed as the area increasing step. In addition to this, natural organic powder and the like can be exemplified as the area increasing agent that can be employed with the water soluble binder.
The dispersion system relating to the first step of the second invention also contains the liquid dispersion medium and the solid disperse phase. The liquid dispersion medium relating to the second invention is one that can constitute the dispersion system along with porous material powder as the solid disperse phase, the area increasing agent and the binder, and can be removed from the molded block by the liquid dispersion medium removing step, so as to increase the surface area of the continuous flow paths in the area increasing step. As the liquid dispersion medium, water is generally employed in the case where the area increasing agent is an agar component. Water includes any of cold water, warm water and hot water. Depending on the selection of the area increasing agent, a volatile solvent, such as an alcohol and the like, can be employed as the liquid dispersion medium.
In the second invention, the mixing ratio of the binder is not particularly limited, and the binder is preferably mixed at a mass ratio of from 1 to 50 parts by mass per 100 parts by mass of the mixture of the porous material powder and the area increasing agent. It is more preferred that the binder is mixed at a mass ratio of from 2 to 30 parts by mass per 100 parts by mass of the mixture of the porous material powder and the area increasing agent. It is further preferred that the binder is mixed at a mass ratio of from 5 to 15 parts by mass per 100 parts by mass of the mixture of the porous material powder and the area increasing agent. The dispersion system may further contain a molding assistant, such as a dispersing agent, a wetting agent and the like.
The adsorbent block obtained by the second invention is formed to have continuous flow paths by binding mainly the porous material powder. The continuous flow path is a flow path that continues from an inlet to an outlet of the air or the like.
In the case where an adsorbent block of a honeycomb form is formed to have cells by the production process of the second invention, a cleaning filter can be obtained by the adsorbent block. The adsorbent block of the cleaning filter is produced by a production process comprising a first step of preparing a paste comprising water having mainly active carbon powder dispersed therein, and molding a molded block with the paste, and a second step of removing water from the molded block to bind mainly the active carbon powder. At this time, the paste contains a binder that is capable of binding the active carbon powder and an area increasing agent that disappears by heating the molded block at a particular temperature, at which the binder does not disappear, and the second step comprises a liquid dispersion medium removing step of removing water, and a heating step of heating the molded block at the particular temperature.
In the production process of the first and second inventions, the molded block may be molded only with the dispersion system, or in alternative, may be formed by fixing the dispersion system on a substrate material, such as metallic plate, e.g., an aluminum alloy and the like, ceramics, paper, wood and the like.
In the production process of the first and second inventions, as the porous material powder as the solid disperse phase, active carbon powder can be employed. In addition to this, silica aerosol, zeolite, bentonite and the like can be employed. By using the porous material powder, a VOC (Volatile Organic Compounds), such as formaldehyde and the like, and an offensive odor component and a harmful component, such as NOx, SOx and the like contained in a gas, such as the air, and impurity ions and the like contained in a liquid, such as water, can be removed by adsorbing on minute pores of the porous material powder.
In the production process of the first and second inventions, when the molded block is obtained by extrusion molding, the disperse system is preferably has a low soft degree (i.e., becomes hard), but in the case where the shrinkage agent or the area increasing agent is an agar component, it is necessary that a large amount of water is added as the liquid dispersion medium for realizing shrinkage and pores in future, and thus the disperse system has a high soft degree (i.e., becomes soft). As a result of the test conducted by the inventors, in the case where active carbon powder is employed as the porous material powder, while depending on the particle diameter of the active carbon powder, the soft degree is preferably from 5 to 20 mm, which is the difference in the position of one end of a sample in the case where the sample having a cylindrical shape having a length of 5 cm and a diameter of 2 mm is formed, and then the center position of the sample is supported at room temperature to bend one end by gravity. When the soft degree is less than 5 mm, the dispersion system is too hard, and the molding of the molded block is not easy. On the other hand, the soft degree exceeds 20 mm, the dimensional stability of the molded block is poor. The soft degree is more preferably from 5 to 10 mm.
According to a result of the test conducted by the inventors, in the production process of the first and second inventions, less than 15 parts by mass of an agar component is preferably contained in 100 parts by mass of active carbon powder, and it is preferred that these are dispersed with from 120 to 250 parts by mass of water. When the amount of the agar component is too large with respect to the proportion of the active carbon powder, the strength of the adsorbent block is difficult to maintain due to disappearance of the agar component in the area increasing step. The proportion of water depends on the proportion of the agar component. Since the agar component is disappeared in the area increasing step, it is not necessary that the agar component is completely dissolved in the dispersion system.
In the production process of the first and second inventions, a photocatalyst, an room temperature oxidation catalyst and the like for oxidation decomposition of an VOC (Volatile Organic Compounds), such as formaldehyde, may be carried on the adsorbent block. In this case, the photocatalyst and the like are dispersed along with the porous material powder in the liquid dispersion medium or are carried on the molded block or the adsorbent block. When it is the case, the offensive odor component and the like adsorbed on the porous material powder are decomposed by the photocatalyst and the like, and the adsorbing ability of the adsorbent block is regenerated. As the photocatalyst, as disclosed in Japanese Patent Laid-Open No. 8-257410 and the like, at least one kind of oxides of Ti, Cu, Zn, La, Mo, V, Sr, Ba, Ce, Sn, Fe, W, Mg and Al, a TiO2xe2x80x94Pd composite oxide, and a sulfide, such as CdS can be employed. As the room temperature oxidation catalyst, at least one kind of a noble metal, such as Pd, Pt, Au, Ag, Rh and the like, an oxide of Mn, Ni, Cu, Fe or the like having an oxidation reduction potential and a composite oxide thereof can be employed. In the case where the photocatalyst is carried, it is preferred that the adsorbent block is irradiated with an ultraviolet ray for oxidation decomposition of a chemical substance, such as ammonia, a hydrocarbon and the like, thus adsorbed. A cathode tube and an LED can be used as the light source. The photocatalyst may also be activated by sunlight. In the case where sunlight is utilized, the adsorbent block is irradiated directly with or indirectly through a mirror or an optical fiber with sunlight taken from the outside.
In the production process of the first and second inventions, extrusion molding, compress ion molding and the like may be employed as the molding method.
In the production process of the first and second inventions, the continuous flow path may be either one extending straight or in a curved manner. It is preferred that the continuous flow path extends straight from the standpoint of a small flow path resistance. In order to produce an adsorbent block having straight continuous flow paths, the adsorbent block may have a honeycomb form. In this case, the molded block of the first step may be formed into a honeycomb form. In order to form the molded block in a honeycomb form, extrusion molding may be employed. The opening part forming the honeycomb form is not limited to a hexagon and may be such a shape that does not impair passage of a gas and a liquid, such as a triangle or a higher polygon or a circular shape, such as an ellipsoid.
On the other hand, when the continuous flow path extends in a curved manner, the air or the like passing through the continuous flow path is liable to collide on the wall constituting the continuous flow path to increase the flow path resistance, but it is considered that the adsorption efficiency is improved. In the case where an adsorbent block having continuous flow paths extending in a curved manner, such manner that a foaming agent is contained in the dispersion system, and the like may be employed. Continuous flow paths formed by connecting gaps each other that may be present among the porous material powder.
The adsorbent block obtained by the production process of the first and second inventions can be used as a cleaning filter in an air cleaning apparatus, such as an air cleaner. In this case, the cleaning filter is preferably provided on the downstream side of a dust collection filter and a dust collection device. This is because powder dusts are removed by a dust collecting filter or the like on the upstream side, so as to prevent clogging of the adsorbent block of the cleaning filter with the powder dusts.
It is preferred that the dust collecting filter that suffers clogging can be exchanged. Accordingly, in the case of an in-vehicle air conditioning apparatus, the dust collecting filter can be mounted as capable of being exchanged in a glove box or the like. Similarly, it is preferred that the cleaning filter can be exchanged. This is because in the case where the cleaning filter is broken or the like, the exchange thereof can be made easily. In order to mount the dust collecting filter and the cleaning filter as capable of being exchanged, it is preferred that these are provided in an air cleaning apparatus or the like by a holder.
The dust collecting filter is not particularly limited in the structure thereof, and a dust collecting material, such as cloth, nonwoven cloth, paper and the like, formed to have a pleated (wave) form can be employed. A dust collecting apparatus employing an electric dust collecting method where a high voltage is applied can also be employed. The dust collecting filter and the cleaning filter are arranged closely, preferably continuously, provided. According to the configuration, both of them can be compactly mounted. The shapes of the dust collecting filter, the cleaning filter and the like are appropriately designed corresponding to an air cleaning apparatus and the like, to which they are applied.
The adsorbent block obtained by the production process of the first and second inventions is demanded, for example when it is used for an in-vehicle air conditioner, to remove at least 40% of various gas components per passage of the air in the vehicle. As the adsorbent block of a honeycomb form that satisfies the demand, one having a proportion of the active carbon powder of 60% by mass or more and an area proportion occupied by the opening part of from 50 to 80% and from 500 to 1,000 cell/inch2 can be used. When it is less than 500 cells/inch2, the extent of the inlet is not sufficient to impair the adsorbing performance.